1. Field of the Invention
The present invention relates to systems for processing return fluid and entrained cuttings.
2. Description of the Related Art
Hydrocarbons such as oil and gas are recovered from a subterranean formation using a wellbore drilled into the formation. When an oil well is drilled, a drilling fluid, commonly referred to as drilling mud, is used to lubricate and cool the drill bit and to carry away cuttings of rock and earth. Commonly, the drilling mud includes water as well as oil, an oil-based carrier, or a diesel-based fluid.
Oily drill cuttings often cannot be discharged directly into the environment due to their adverse effect upon the environment and, therefore, must be processed for disposal in costly disposal wells. Additionally, because of the great value of the residual oil and chemicals contained in them, it has been a common practice to treat the oil drill cuttings in order to produce a solid material that can be disposed into the environment surrounding the well site or returned into the well from which it came without injury to the environment or interference with the well.
One method of treating these oily drill cuttings has been through the use of a chemical washing system. In this system, the oily drill cuttings are treated with various chemicals, including detergents, with relatively intense mixing. Then, this mixture is resolved into relatively oil-free solids (i.e., the drill cuttings) and a recovered liquid phase which is a mixture of water, oil, and the detergents which were employed in the chemical wash system. Burial or re-injection then disposes of the solids. However, these solids may still contain sufficient oil and/or chemicals that, upon contact with bodies of water, such as surface waters, lakes or the ocean, produce unacceptable levels of toxins detrimental to preserving the environment in the best possible form. In addition, the liquid phase must be treated to separate the oil from the bulk water phase so that the water portion can be discharged or otherwise disposed without pollution problems. The separated oil and expensive drilling fluids are usually recovered and utilized for various uses such as fuel or be returned into the blending of additional oil based drilling muds and the like.
Conventional chemical wash procedures for treating oily drill cuttings have certain disadvantages, especially when they are to be employed on offshore drilling platforms. For example, large amounts of chemicals must be transported at great expense to offshore facilities. In addition, these offshore platforms do not have any surplus of steam, gas, electrical, or other energy sources. Thus, a procedure for treating the oily drill cuttings must be self-sufficient relative to the operations on the offshore platforms.
Centrifugal separators are widely used as a very efficient method for separating fluids from solids. In general, vertical, centrifugal separators such as is described in U.S. Pat. No. 5,256,289 include a housing containing a drive mechanism to which is connected both a flight assembly and a screen assembly. The separator further includes an inlet for induction of the material to be separated. Induced material is captured by the flight screen assembly, separation occurring as the material migrates downwardly with liquids or very small particles present on or in the material being forced outwardly through a fine screen into a space between the screen and the housing by centrifugal force. The majority of the liquids are then drawn off and the solids are generally ejected from an outlet assembly located below the rotor drive assembly. The outlet assembly usually is defined as a conical discharge bin for depositing the solids in a container or further conveyed to other locations for disposition, thereby making the dryer quite high.
In addition, the treatment procedure for the oily drill cuttings must be safe to operate, not require extensive retention time, operate without interference or hindrance to the drilling operations conducted on the offshore platform, while yet producing solids from the drill cuttings which can be disposed of safely and without any injury to the environment at the drilling site. In addition, the system for the treatment of oily drill cuttings at the drilling site, and especially on an offshore platform, must not require a constant supply of chemicals, fuel, nitrogen or other materials for its operation. The present invention addresses these and other drawbacks of the prior art.